Field
The present disclosure relates to power amplifiers in radio-frequency applications.
Description of the Related Art
Power amplifiers (PA) are widely used in networks in order to set the transmission power level of an information-bearing signal. For example, PAs are used to set the pulse emission energy of lasers in optical networks. PAs are also included in various wireless network devices—such as base stations and mobile devices—in order to set the transmission power level of a radio-frequency (RF) signal. PAs are also used in local area networks in order to enable wired and wireless connectivity of various devices.
Managing PA operation is important in a mobile device that uses a battery, because the power consumption of the PA often has a substantial impact on battery life. However, satisfying power consumption goals can be detrimental to other goals, such as linearity, which affects signal integrity and error control in data packets.
For example, bias circuitry is often provided to support the gain function of a PA, in addition to establishing the quiescent on-state conditions of PA transistors. Preferably, bias conditions support the PA in providing relatively constant gain, as a function of time, across a duration used to transmit a data packet. According to a first approach, bias circuitry is configured to operate using a lower voltage supply than the PA transistor in order to reduce power consumption.
A second approach includes switching the PA and the bias circuitry from an off-state to an on-state on demand (and then back to the off-state), so that the PA and bias circuitry do not dissipate power when data is not being transmitted. However, PA linearity is adversely affected by combining the first and second approaches. Nonlinear changes in the respective temperatures of the bias circuitry and the PA stem from the different voltage supply levels provided to each, and a switch from an off-state to an on-state. In turn, the power density in the PA does not track the power density in the bias circuitry, which causes a non-linear variation in gain that can be measured as a degradation in error vector magnitude (EVM).